1. Field of the Invention
This invention relates to a multi-head laser engraving machine having a laser, at least two exposure heads each with an optical system/deflection unit for directing part of the laser beam energy to a working area of a workpiece surface as an engraving beam, and a control unit.
2. Description of the Related Art
Such multi-head laser engraving machines, which are typically executed as two-head machines, are used for example for efficiently inscribing plastic parts, for example radio panels (Ulrich Over, Ulrich Hartmann, "Laserbeschriftung .mu.-genau," supplement to Hanser Fachzeitschriften, October 1991, pages LS113, LS114, Carl Hanser Verlag, Munich).
The laser is typically an Nd:YAG laser with a power of 50 to 100 watts. One exposure head is preceded by a beam splitter, the other exposure head by a tilted mirror. A galvanometer deflection unit with a following optical system present in each exposure head moves the beam within the working area on a workpiece surface. By on-off control of the laser beam the workpiece surface is engraved or inscribed in each working area. Since laser inscription is a frequent application for such an apparatus, such an exposure head is also called an inscription head or deflection head.
The deflection units in each exposure head are typically moved in synchronism so that with corresponding control of the laser the same inscription is done in each working area.
As an alternative embodiment, a swiveling mirror or the like can be provided, instead of a beam splitter, for the exposure head directly following the laser so that the total energy of the laser beam is directed by the swiveling mirror via the deflection unit to the first working area, or directed by the tilted mirror and the second exposure head to the working area associated with the latter. In this way one can engrave different patterns with the two exposure heads, but only staggered in time. In the prior art there are thus only the two mutually exclusive possibilities of obtaining the same inscription in the working areas using a beam splitter or obtaining independent inscription using a beam changeover switch, but not both simultaneously.